1. Field of the Invention
The present invention is generally related to a marine steering system and, more particularly, to an actuator which combines a linear actuator and a spool valve in a compact structure for use in a steering system of a marine propulsion device.
2. Description of the Related Art
Those skilled in the art of marine propulsion systems are aware of many different steering devices that can be used to cause the rotation of a marine propulsion device about a generally vertical steering axis. Typically, a cable system is incorporated in the steering system and connects a steering arm of a marine propulsion device to a manually controllable steering mechanism, such as a steering wheel. Other types of steering systems incorporate hydraulically assisted components which use pressurized hydraulic fluid to provide force in order to assist the operator of a marine vessel in accomplishing steering maneuvers. Some hydraulic steering systems use a pump mechanically attached to a steering wheel and a hydraulic actuator attached to the marine propulsion device. Other types of hydraulic steering systems use a mechanically or electrically driven hydraulic pump to provide pressurized hydraulic fluid that is then ported, by suitable valves, to actuators that effect the steering maneuvers.
In certain marine steering systems, two or more marine propulsion devices can be individually rotated about their respective steering axes independently so that complicated maneuvers can be accomplished by selectively directing the propeller thrusts of the marine propulsion devices in selected directions while also controlling the forward and reverse rotation of the propellers in order to provide suitable thrust vectors that allow the marine vessel to be maneuvered. These types of systems typically use a joystick associated with a microprocessor to interpret commands from the operator of a marine vessel and calculate the necessary individual thrust vectors necessary to accomplish those commanded maneuvers.
U.S. Pat. No. 3,645,296, which issued to Adams on Feb. 29, 1972, describes a power assisted steering system. A power assisted rack and pinion steering system includes a housing, relatively rotatable torque input and output shafts mounted for rotation in the housing, a pinion mounted for joint rotation on the torque output shaft, a rack engaging the pinion and a fluid valve assembly for controlling the flow of fluid to and from the opposite ends of a double-acting servomotor also connected to the rack for assisting in the movement thereof. The valve assembly comprises a circumferentially grooved spool valve connected to one of the shafts for axial movement, such movement occurring when the shafts are rotated relative to one another. Axial movement of the spool valve establishes fluid communication between a power fluid pump and the servomotor for powered movement of the servomotor and hence the rack.
U.S. Pat. No. 3,712,582, which issued to Moesta on Jan. 23, 1973, describes a fluid flow control valve and linear actuator therefore. A support housing having a cylindrical bore in which a complimentary cylindrical spool valve is carried and screw-threadedly engaged with the housing is described. The valve is rotated by a drive motor for linear movement of the valve in the bore. An inlet port and an outlet port open to the bore so that communication therebetween is accurately controlled by the linear positioning of the spool valve. A pulse drum structure is connected with and rotates with the spool valve and has sensor points thereon which, as the pulse drum rotates with the valve, pass by a sensing device which is thus enabled to sense linear change of position of the drum and hence its associated valve.
U.S. Pat. No. 4,200,030, which issued to Elser on Apr. 29, 1980, describes a servo steering gear. A power steering gear mechanism is disclosed having conventional elements such as a double acting cylinder in a housing, a piston with a gear rack geared to a gear sector, and threaded bore in the piston having a worm shaft, wherein a steering shaft operates a rotary valve spool with which it is integral, in rotation relative a fixed valve sleeve carried by the worm shaft and wherein a torque rod connects the worm shaft to the steering spindle and passes through the worm shaft.
U.S. Pat. No. 4,841,790, which issued to Williston et al. on Jun. 27, 1989, describes an electromechanical actuator. The actuator is particularly attractive for vehicle steering applications and includes a case having a cover part rigidly attached to a housing part and an output rod supported on the case for linear shiftable movement along a primary axis of the case. An electric motor is mounted on the housing part of the case with a shaft of the motor supporting in cantilever fashion a pinion in a gear chamber of the case between the housing and covered parts.
U.S. Pat. No. 5,947,155, which issued to Miki et al. on Sep. 7, 1999, describes a linear solenoid valve. The valve is composed of a pressure regulating section and an actuator section. In the pressure regulating section, a valve spool is slidably disposed and is biased in one direction by a single elastic member. The actuator section generates a thrust force and transmits that generated thrust force in an opposite direction to the pressure regulating section via a shaft.
U.S. Pat. No. 6,065,451, which issued to Lebrun on May 23, 2000, describes a bypass valve with a constant force-versus-position actuator. A control arrangement for a fuel system having a fuel pump for supplying fuel through a variable orifice flow metering valve to an engine main fuel control is described. The control portion controls the fuel pressure differential across an orifice of the metering valve. A head sensor includes a movable diaphragm, a bypass valve for diverting fuel from the fuel pump away from the metering valve, and a coupling between the diaphragm and the bypass valve whereby the bypass valve opens and closes in response to diaphragm motion.
U.S. Pat. No. 6,234,853, which issued to Lanyi et al. on May 22, 2001, discloses a simplified docking method and apparatus for a multiple engine marine vessel. The system is provided which utilizes the marine propulsion unit of a marine vessel, under the control of an engine control unit that receives command signals from a joystick or push button device, to respond to a maneuver command from the marine operator. The docking system does not require additional propulsion devices other than those normally used to operate the marine vessel under normal conditions. The docking or maneuvering system of the invention uses two marine propulsion units to respond to an operator's command signal and allows the operator to select forward or reverse commands in combination with clockwise or counter-clockwise rotational commands either in combination with each other or alone.
U.S. Pat. No. 6,354,184, which issued to Hansen et al. on Mar. 12, 2002, describes a power machine with valve mount for valve assembly. A power machine or a skid steer loader that is driven by an engine and has a hydraulic pump, hydraulic fluid conduit, a hydraulic motor in fluid communication with a hydraulic fluid conduit and a valve that is operated or actuated by linear actuator such that the linear actuator is mounted directly on the valve block is described.
U.S. Reissued Pat. RE39,032, which issued to Gonring et al. on Mar. 21, 2006, discloses a multi-purpose control mechanism for a marine vessel. The mechanism allows the operator of a marine vessel to use the mechanism as both a standard throttle and gear selection device and, alternatively, as a multi-axes joystick command device. The control mechanism comprises a base portion and a level that is movable relative to the base portion along with a distal member that is attached to the lever for rotation about a central axis of the lever. A primary control signal is provided by the multi-purpose control mechanism when the marine vessel is operated in a first mode in which the control signal provides information relating to engine speed and gear selection. The mechanism can also operate in a second or docking mode and provide first, second and third secondary control signals relating to desired maneuvers of the marine vessel.
U.S. Pat. No. 7,131,385, which issued to Ehlers et al. on Nov. 7, 2006, discloses a method for braking a vessel with two marine propulsion devices. The method comprises steps that rotate two marine propulsion devices about their respective axes in order to increase the hydrodynamic resistance of the marine propulsion devices as they move through the water with the marine vessel. This increased resistance exerts a braking thrust on the marine vessel. Various techniques and procedures can be used to determine the absolute magnitudes of the angular magnitudes by which the marine propulsion devices are rotated.
U.S. Pat. No. 7,168,360, which issued to Massaccesi et al. on Jan. 30, 2007, describes a steering system actuator for a vehicle with at least three steered wheels. A linear actuator for vehicle powered steering systems with at least three steered wheels of a double-acting type that comprises a cylindrical body, closed and open ends, is disclosed. It also comprises a piston, accommodated inside the cylindrical body axially slidable between the ends, and a stem which is rigidly associated with the piston, coaxial to the cylindrical body, and protruding from at least one of the ends. A piston divides the cylindrical body into two chambers. Each chamber is provided with an inflow/outflow opening formed at the two opposite ends. At least one pair of one-way valves, provided in the piston with a respective inlet connected to a respective chamber and outlets mutually connected, each valve having a step slidably accommodated in the respective inlet with one end associated with a respective flow control element and the opposite end that protrudes externally from the piston, so as to open a respective valve.
U.S. patent application Ser. No. 11/602,532, which was filed by Heitzer on Nov. 21, 2006, describes a valve device for a hydraulic servo steering arrangement. It includes two valve elements which can be rotated from a neutral position relative to each other in order to thereby achieve the superimposition of an additional steering moment. The valve device further includes a linear actuator and a gear coupling the two valve elements to each other. The gear converts a linear stroke of the linear actuator into rotation. The gear includes a first cog wheel with teeth inclined in a first direction in relation to the actual direction of the cog wheel. The first cog wheel is coupled to the first valve element. The gear further includes a second cog wheel with teeth inclined in a second direction opposed to the first direction. The second cog wheel is axially displaceable by the linear actuator.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
It would be significantly beneficial if a compact device could be provided which provides a marine steering system with inherent mechanical feedback that coordinates the movement of a hydraulic actuator and a hydraulic valve under the control of the linear actuator which, in turn, is controlled by signals received from a microprocessor.